Have replaced the pressure switch, still the same

by Tom Kearns
(Newport RI USA)

Compressor will not shut off. Replaced pressure switch with new one ($75.00) and still wont' shut off automatically, when shut off manually and then flipped to auto it stays shut off untill pressure is low enough to turn back on, compressor runs to full pressure and then has to be turned off manually, so it works in one direction (turning itself on) but not turning itself off. Process reapeats. There are no leaks the compressor hold steady when not being used. Not sure what to do next.


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Bill says....

The device that turns the air compressor on and off is the pressure switch.

If your compressor reaches cut out pressure and it continues to run, power must be getting to the motor through the pressure switch. Therefore, the pressure switch has failed, has failed to switch at cut out pressure level, or has been wired improperly.

Use your multimeter to check the power line to the motor once the pressure reaches normal cut out. If power is still flowing to the motor, something is not right with your pressure switch.

Cheers,

Bill

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Dec 18, 2015
Wiring
by: Anonymous

So the air compressor continues to build pressure past the cut off point. I was having the same issue so what i did was buy a new control switch. Then it continued to have the same problem. It would continue to fill past the cut off point until the SRV blew. The Control switch is mainly mechanical if you look at it. I was using a condor MDR11. I noticed a small spring loaded switch on the bottom that can become obstructed if you jam the extra ground wire in there which is easy to do because the ground is just infront of the switch. Check to make sure your wires are tidy, and not jammed into the box where they can short or obstruct any of the mechanical springs or switches. Hope that helps.

May 27, 2011
Pressure switch
by: Tom

Question, when a compressor states max pressure 150 psi but wont get above 140psi, could that be the problem with the pressure switch not reaching the required pressure to shut off? Or is the max pressure is what the compressor will do and the factory settings are 140, either way where is the pressure going once it reachs the 140 and why doesnt it build higher to reach blow off threshold?

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Visit the TROUBLESHOOTING page and read the info on the page linked from " won't build pressure ".


May 19, 2011
Question regarding checking electrical
by: Anonymous

Have done a continuity check and all is good per the wiring diagram. What are the odds that I got sent a faulty switch. Also, I am curious how the switch reads the pressure to shut off, could there be somthing else that is sending the signal like the pressure itself that is not reaching the switch. Is the switch purely electrical, how does it read the pressure. Remember the switch is new. I also replaced this switch about 2 years ago with the same problem and it has worked fine until now. This is a Craftsman 6hp 30 gallon single cylinder oil free compressor. Please help

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Pressure switches usually have a diaphragm that reacts to the pressure in the system, and opening an closing points to stop or all electrical flow.

Since a new switch may be the least expensive solution, sure, try another one.

The thing is, if the power flows to the compressor motor with the switch trips on, and stops when the switch trips off, then the switch is likely not your problem.


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Can I run two compressors on one pressure switch if they are all connected?

by Stephen
(Snellville Ga)

I have two commercial compressors with three tanks. All hooked together. There will be a starter for each motor. Can I run each motor with one pressure switch? This is a single phase 230 volt system. One compressor is 7 1/2hp the other is 10hp. Any help at all would be very appreciated. The compressor cuts out but wont come back on by itself when the pressure drops. Pressure switch?

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Bill says...

If the switch can carry the load of two fairly large electric motors starting at the same time, then yes, you could conceivable have the same switch start both compressors at the same time... I think?

Typical installations when folks have two compressors for one air main are that one compressor kicks on at, say, 90 PSI, and kicks off at 120 PSI. As long as the one can maintain the air needed, the secondary, set for cut in at 85 PSI, need not start. It's only when the primary can't keep up demand that the secondary starts. Every few months, the pressure settings are switched, so the secondary becomes the primary... and so on.

About the non-start, when the pressure drops to cut in, does the pressure switch trip? Is there power flowing from the switch to the motor when the pressure is below cut in pressure level? If not, yup, it's probably the switch.

Cheers,

Bill

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Jan 02, 2014
neilson 2.5hp 50 litre air compressor cannot keep up
by: Anonymous

my girlfriend brought me a neilsons 2.5hp 50 litre
air compressor for Christmas I am trying to run a neilsons portable sandblaster of it, itneeds 90-125 psi as soon as the pressure is right and I use the sandblaster I have about 5 seconds before the pressure drops to low I have adjusted the air flow volve with no joy can you help
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What is the air flow demand of your portable sandblaster? Your compressor will flow about 8-10 CFM at best. I suspect your sandblaster will require quite a bit more than that to operate correctly.

Therefore, I suspect your air compressor is too small for the air tool you are trying to run.

Bill

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pressure is set at 149 and 175

by Charles
(Lewes de.)

gas station air compressor

gas station air compressor

I bought a gas station air compressor that has a max pressure of 200psi.I want to lower it to 160psi so I can purchase a regulator at Harbour Freight that has a max of 160psi,can I do it.
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Charles, sure you can, if your pressure switch is an adjustable kind.

It were my compressor, I'd leave the pressure settings where they are, and get an air regulator that may cost a bit more but has a 200 PSI rating.

Why, because you then have a longer period of using compressed air that has been regulated down to your air tool minimum operating pressure before the compressor has to start and rebuild pressure.

If, however, your concern is safety, if the compressor has been built for a 200 PSI cut out, then it should be fine, unless there is degradation in the various compressor components.

Bill


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Help wiring 5 hp compressor pressure switch

motor has black, white and ground. If using my clothes drier receptacle would i use black, red, white and ground. Does the other 2 contacts of the pressur switch use black and red ie no white to give the 220 or do you use the white and stack the black and red to the contact. 4 CONTACTS MOTOR WHITE MOTOR BLACK AND OTHER TWO ON SWITCH ?
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I've posted this Mr/Ms mgdeathe in the hope that an electrician can respond.

I'm not one, and have too high a respect for the speed with which 220 volts can kill (120 volts too for that matter) to offer you wiring advice.

Cheers,

Bill

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Locating under pressure valve

by betty
(va)

My craftsman 30 gallon 6 hp compressor will run until it begins to kick the motor back on and it blows the breaker. I'm trying to locate the under pressure valve w/o a diagram. Could you please tell me where precisely it's located or where I can locate a diagram for the whole compressor?

Thanks






Bill says...

Hi again Betty. I think you mean the pressure switch.

Info on the pressure switch is here.

Cheers,

Bill

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